Sometimes it seems as if almost every device manufactured today includes electronic circuitry. For example, microprocessors are present in a wide array of products, including such disparate items as high-end computer systems, body-implantable medical systems, kitchen toasters, and simple children toys.
For many electronic systems, achieving small size is highly desired. Accordingly, numerous advancements in the miniaturization of electronic systems have been achieved over the last few decades. Microelectronic circuits, including for example silicon integrated circuits, have become ubiquitous. Integrated circuits are miniature electronic circuits manufactured on a thin substrate of semiconductor material. Typically, multiple circuits are manufactured on a single semiconductor wafer, and the individual circuits are then separated into what is referred to as a chip or die. Die sizes vary widely, although die sizes of about 5 mm to 15 mm per edge are common. The die is typically placed into a package, and small wires are connected between the lead frame of the package and bond pads on the semiconductor die.
The scale of wires and bonding pads used in semiconductors is relatively small. For example, a typical bond pad is a square pad of about 35 micrometer to 50 micrometer on a side. Connection between the bond pad and leads of the device is via 15-micrometer diameter bond wires that are ultrasonically bonded to the bond pad and a lead-connecting portion of a lead frame. Unfortunately, even at these sizes, the space taken up by the bond pads has become a limiting factor in some chip designs. For example, one-tenth of the available semiconductor area can be lost to bond pads. Providing higher density interconnect between the semiconductor die and the package has proven challenging, and typically bond pads are limited to rows of two pads on each side of the die due to the wire bond geometry.
The use of multiple die in a single package is also becoming more common. Interconnect requirements are accordingly increased, as wire bonding between die and from die to package are both required.
Accordingly, there is a need for new interconnection technology that can provide significant improvements in interconnection density.